Get rid of @/meta blocks in {CUDA,}ChaChaKeystream docstrings

Get rid of `meta` blocks in docstrings, since they show up in the REPL.
Trailing `meta` blocks also show up in the HTML API documentation, which
we don't really want.

Author: kernelmethod

src/cuda_keystream.jl

@@ -14,24 +14,12 @@ generator for GPU CRNG.
 Create a `CUDAChaChaStream` with a randomized key, and
 sample some random numbers with it:
 
-```@meta
-DocTestSetup = quote
-    using CUDA
-    using ChaChaCiphers
-    using Random
-end
-```
-
 ```julia
 julia> rng = CUDAChaChaStream();
 
 julia> x = CuVector{Float32}(undef, 2^10);
 ```
 
-```@meta
-DocTestSetup = nothing
-```
-
 See also: [`ChaChaStream`](@ref)
 """
 mutable struct CUDAChaChaStream <: AbstractChaChaStream

src/keystream.jl

@@ -15,21 +15,14 @@ generation functions.
 
 Create a `ChaChaStream` with a randomly-generated key and nonce:
 
-```@meta
-DocTestSetup = quote
-    using ChaChaCiphers
-    using Random
-end
-```
-
-```jldoctest
+```jldoctest; setup = :(using ChaChaCiphers, Random)
 julia> stream = ChaCha20Stream();
 ```
 
 Create a `ChaChaStream` with a pre-specified key and nonce, and
 use it to generate random data:
 
-```jldoctest
+```jldoctest; setup = :(using ChaChaCiphers, Random)
 julia> key = UInt32.([
           0xe2e39848, 0x70bb974d, 0x845f88b4, 0xb30725e4,
           0x15c309dc, 0x72d545bb, 0x466e99e3, 0x6a759f91
@@ -46,10 +39,6 @@ julia> randstring(stream, 'a':'z', 8)
 "klmptewr"
 ```
 
-```@meta
-DocTestSetup = nothing
-```
-
 See also: [`CUDAChaChaStream`](@ref)
 """
 mutable struct ChaChaStream <: AbstractChaChaStream